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Monday, 25 June 2012

NASCOM-2 Restoration Project

When I began the restoration of my 1978 vintage NASCOM, I assumed I would need a source of spare parts, and so began hunting the web for other NASCOM owners or units up for sale. Not surprisingly there was nothing. Then one day a message popped into my inbox. Alec Stansfield in the UK had a unit he wanted rid of. Alec's NASCOM is now safely stowed in my (loft) hackspace. (My thanks to the WWW NASCOM home page for making the connection).

By the time I received the unit I had managed to fix my NASCOM without anything other than a couple of new capacitors on the PSU. So here I am, with a second NASCOM on my hands, wondering what to do next? It seems obvious .... another NASCOM must be restored!

A preliminary poke around inside the home made wooden case revealed many corroded components. Yet after opening the case, disconnecting the PSU and doing a bench test, I was amazed to find that despite the severe corrosion around several capacitors, the PSU is working (for short periods of time at least). Levels on all outputs (+12v, +5v, 0v, -5v and -12v) are correct. Spot the four LEDs shining brightly.

This all bodes well for further testing. If the unit can boot, my plan is to replicate the design of the original wooden case but in clear Perspex so that it is suitable as a museum exhibit.

Alec tells me that the unit has a rich history: As well as building the NASCOM, Alec designed and built a series of enhancements. In brief: the additional board under the keyboard is an 8 bit A-D and D-A card. The 1/4 inch jack sockets were input and output for his guitar. The pots (he remembers) allowed control over levels and the amount of signal fed back from the output to the input. The rectangular hole was where a joystick used to sit which also was used to control sound parameters via software. He used the system as an echo machine with his band! He wrote some assembler code (probably now in an EPROM) which sampled the guitar input, used the RAM like a tape loop, and output the sound a controlled delay later. He thinks he used to change the NASCOM boot address via some DIP switches to run my echo machine code - but it's too long ago for him to remember all the details. The EPROM piggy back board allowed him to have two firmware EPROMS in the system and switch between the two. The other expansion board (mounted atop the main board) is a monochrome hi-res graphics card which he says he "knocked up". It worked - but he can't remember much about it. He says that I should find circuits for both boards among the folders of notes that came with the unit.

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About NASCOM

The Nascom 1 and 2 were single-board computer kits issued in 1977 and 1979, respectively, based on the Zilog Z80 and including a keyboard and video interface, a serial port that could be used to store data on a tape cassette using the Kansas City standard, and two 8-bit parallel ports. To minimize cost, the buyer had to assemble a Nascom by hand-soldering about 3,000 joints on the single circuit board.

Z80

"The Z80 was an improved implementation of the Intel 8080 architecture, which was faster, more capable, and much cheaper; alongside the 6502 it was one of the most popular 8-bit processors for general purpose microcomputers and other applications. It was used in the Nintendo Game Boy, the Sinclair ZX80, ZX81, ZX Spectrum and the Amstrad CPC home computers as well as the MSX architecture and the Tandy TRS-80 series—among many others. More so than simply sparking improvements in the budding field of home computing and gaming, the Z-80 also sparked a revolution in electronic music, as the first truly programmable polyphonic synthesizers (as well as their peripherals) relied heavily on implementations of this CPU." --- Wikipedia